This application claims the priority of Japanese patent document 9-358450, filed Dec. 25, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a control apparatus for use in an internal combustion engine, having failure diagnostic device which diagnoses the failure of a swirl control valve. In particular, the control apparatus according to the invention diagnoses a failure of the swirl control valve for imparting a swirl (rotating) flow to an intake air flow to an in-cylinder injection engine, and assures proper operation of the engine during the failure.
In a conventional in-cylinder injection type engine, since lean combustion is necessary to maintain an air-fuel (A/F) ratio of more than 40, in the combustion chamber of a cylinder, a degree of gas fluidity (called a swirl or tumble) is provided. Various techniques can achieve such gas fluidity; in general, however, a combination of the shape of the air intake conduit and a swirl control valve are used to generate a proper gas fluidity.
A conventional internal combustion engine providing such a swirl control valve is disclosed, for example, in Japanese patent application publication No. Hei 5-31649. In that arrangement, in order to avoid degrading operability of the engine, the pressure in the air intake conduit is detected, for controlling a negative pressure change-over valve and alternation of an air fuel ratio target value. In this conventional prior technique, when the swirl control valve cannot be maintained in a closed state, operation of the change-over valve and the alternation of the air-fuel ratio target value are carried out. However, a diagnosis of whether or not the swirl control valve itself is operating normally is not provided for.
It is well known that at a full open state of a swirl control valve such as described above, very little swirl is generated in the intake air flow. On the other hand at a nearby fully closed state, the amount of swirl is large. Further, when the air-fuel ratio is controlled to a lean air-fuel ratio (relative to a stoichiometric air-fuel ratio), it has known that the amount of HC (hydro-carbon) in the exhaust gas varies inversely with the occurrence of the swirl by the swirl control valve.
Accordingly, when an engine is operated at a lean air-fuel ratio, control of the swirl control valve has a large effect on operability of the engine especially with regard to exhaust gas content. Thus, diagnosis whether the swirl control valve is operating normally is extremely important for controlling engine performance and improving fuel combustion.
Japanese patent application laid-open publication No. Hei 8-74583 discloses a technique for improving the exhaust gas characteristic in the lean combustion operation control for an internal combustion engine, by diagnosing the operation of the swirl control valve itself. In this technique, a signal corresponding to the actual valve opening degree in response to a swirl control valve opening command signal based on the operating condition of the internal combustion engine (for example a detected signal such as a pressure etc. of an air intake conduit in the vicinity of the swirl control valve, according to a pressure sensor) is compared with a predetermined standard opening degree characteristic, and it is determined that an abnormality of the swirl control valve has occurred when there is a deviation of more than a predetermined value.
In general, the greater the extent to which the amount of swirl in the air flow (swirl number) supplied to an engine combustion chamber increases naturally with increasing air amount, the more the engine becomes a high speed and a high torque. Accordingly, it is necessary to be able to control a small opening of the swirl control valve when the engine speed and torque are high. Moreover, it is necessary to control the opening degree of the swirl control valve taking into the consideration the operation conditions and the combustion condition, under other conditions as well.
The stability of the combustion of the engine, as well as the incidence of exhaust smoke and HC (hydro-carbon) etc., depend on the fuel injection timing and the ignition timing of the fuel injector, which must be taken into consideration in combustion control. In particular, the stability of the combustion of the engine and the occurrence of HC (hydro-carbon) etc. are affected by the amount of swirl (the "swirl number"). By selecting the swirl flow, it is known that the most stable combustion and the minimum occurrence of HC (hydrocarbon) can be achieved. Further, it is also known that the stability of the combustion and the occurrence of HC (hydrocarbon) etc. are affected by the pressure of the fuel which is injected from the fuel injector. As a result, to adjust the swirl flow in opening and closing control of the swirl control valve, it is necessary take into consideration the combustion condition and the fuel pressure to achieve stability of combustion etc. Further, when an abnormality occurs in a control system etc. of the engine, in order to remove the factors which can degrade engine operability (such as the knocking), it is necessary to control the ignition timing in a suitable manner.
However, in the above described conventional prior art techniques, with regard to the operating condition of the internal combustion engine, a signal corresponding to the actual valve opening degree (such as the pressure change in the air intake conduit according to a pressure sensor) in response to a swirl control valve opening command signal is detected. This signal is then compared with a previously determined standard opening degree characteristic, and it is determined that an abnormality of the swirl control valve exists when there is a deviation which exceeds a predetermined value. However, there is no consideration of the abnormality or failure etc. of the swirl control valve itself; accordingly it is impossible to curtail exactly the degradation of engine operability during the abnormality or failure.